The invention relates to a butterfly valve that can be used under a wide variety of fluid temperature, chemical and abrasion conditions. Butterfly valves in general are a popular type of valve because of the simplicity of the construction thereof, and because they are inexpensive to make. Conventional butterfly valves, such as shown in U.S. Pat. Nos. 2,986,373 and 3,583,668, are very practical, under many conditions; however, since they require the use of elastomers around the periphery of the vane or at the valve seat to effect sealing, they have limited use. Such conventional valves cannot normally be used where the temperature is above about 300.degree. F. of where adverse chemical or abrasive conditions exist. Other valves, such as shown in U.S. Pat. No. 3,931,955, may attain circular line contact; however, when wear occurs, the valve seat must be replaced, a difficult process.
According to the present invention, a butterfly valve is provided that is useful in environments with temperatures in excess of 1000.degree. F. and in environments where solvents, chemical reagents and abrasive fluids are to be valved. The valve of the invention provides for metal-to-metal sealing of the vane and the valve seat, no elastomers being necessary to effect a fluid-tight seal. An annular metal valve seat is mounted in a valve body and cooperates with a metal disc vane. The vane is so constructed and mounted for rotation within the valve body that circular line contact is provided between the valve seat member and the vane. This circular line contact makes the utilization of a metal-to-metal seal possible because the valve seat need be deformed only very, very slightly in order to have good contact pressure between itself and the vane at all points of the contacting line. This is in stark contrast to vanes that do not have a circular contact line, wherein high pressure is required at the points where the seal has to be deformed the most, in order to establish a much lower contact pressure at other points in the contacting line.
According to the present invention, the vane is formed as a conical angle-transported disc, the disc having a thickness approximately 1/10 - 1/20 its diameter. A conical angle-transported disc is a disc which may be considered to be a portion of a cone having spaced parallel faces of different diameter and a center line through the circular faces of different diameter being perpendicular to the faces; then the center line is angle-transported so that the center line forms an angle of greater than 0.degree. with a line perpendicular to the upper and lower faces (the center line no longer being perpendicular to the upper and lower faces). While there have been proposals to provide circular line contact with a cylindrical angle-transported disc vane, there have been problems with such an arrangement since there is an awkward tightness of the vane as it passes through the seat, at about an 8.degree. angle, prior to seating. This tightness causes the seat to be moved outwardly as the vane passes through it, and, thus, there is excessive leakage where the vane has pushed the seat away. According to the present invention, these problems have been avoided while still providing true circular line contact, by providing a conical angle-transported disc instead of a cylindrical angle-transported disc. (A cylindrical angle-transported disc is a disc that may be considered to originally be a portion of a cylinder having spaced parallel circular faces with a center line extending through the centers of the two faces and perpendicular to the faces; the center line is then transported through an angle so that it is disposed at an angle greater than 0.degree. with respect to a line that is perpendicular to the two faces.) The conical angle-transported disc has an upper face of a diameter D' slightly less, approximately 1/50 - 1/100, than the diameter D of the lower face and an angle .alpha. of between 20.degree. and 40.degree. being formed between a centerline through the upper and lower faces and a line E perpendicular to the upper and lower faces. The vane is rotatable about an axis of rotation perpendicular to the direction of fluid flow through the valve body, and the circumferential edges on a diameter of the upper face perpendicular to the axis of rotation have an angle of generally about .alpha..
It is the primary object of the present invention to provide an improved butterfly valve having metal-to-metal sealing contact. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.